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With out completely removing the cranks and bottom bracket, how can I tell when it's time to replace my bottom bracket?

The current symptom is a slightly 'rough' feeling when I pedal. It's not constant, and it's not the pedals - I've swapped them out recently with nearly new ones.

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up vote 13 down vote accepted
  • Pull your cranks laterally. Do they move?
  • Give your cranks a good spin, preferably without the chain. Hear any unusual grinding noise or little clicks ?

If you answered no to both questions, keep pedalling. You're still fine.

It would be nice if the BB was always smooth as butter, but a little rough doesn't mean it's broken.

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I am going to assume we are dealing w/ a JIS style square taper bottom bracket for this issue. At least, I am going to address it as such.

If it is a cartridge style BB you really have no choice in repairing the less than perfect feel so either accept the roughness and look at a new one next season or switch her out when you feel.

If it is a loose ball and you are partial to it (ex: ti spindle) the roughness is a sign that you should get on servicing it asap. The roughness can come from contamination of the grease and result in the spindle race pitting and the cup races pitting as well. Once these are pitted you will most likely never get it back to that silky smooth feeling you so desire.

In reality, chances are it is a cartridge JIS BB.

Domsterr is spot on with the 'lateral' play issue. To add to the recommendation of spinning the cranks I would add the following:

  • take the chain off of the chain rings, when giving it a spin, as the chain will interfere with your ability to assess by ear.

  • hold the down tube or seat tube and 'feel' for the grinding through the frame. You would be surprised how effective that is. I use it regularly for assessing hub condition.

That's about all I've got.

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It is an older style shimano square taper BB. – Gary.Ray Oct 11 '10 at 22:33
2  
depending on where you live (ex: I live in Canada, there will be a crap ton of salt on the road soon) and how late into the winter you ride I would recommend you look at replacement next spring. No point to subjecting it to winters wrath (again, if you live in an area such as I do). – tplunket Oct 13 '10 at 0:37

I have one suggestion to add to this thread...

...the best way to check cartridge bearings is to check them. Remove the cranks. No need to remove bottom brackets for this, but if you have the tools available you might as well. This is a good opportunity to clean the BB face and shell and check for any corrosion. To check the bearings simply spin them with your finger. You will very quickly notice if there is any play or roughness. If they feel buttery smooth, then you have nothing to worry about. If they spin freely, you need to think about replacing them, or stripping and re-greasing (if you are up to it and you have the necessary tools). It is normal for one side to give out before the other, so it will be obvious when this happens. Personally, given the low cost of new brackets, I think it better just to replace. In fact, you can do this as part of your scheduled maintenance depending on your mileage and the quality of parts used. I just did mine (FSA MegaExo) after 3,000 miles (DS was spinning freely, NDS was ok), so I know I am unlikely to get another 3,000 miles before they need doing again. As mentioned above, you can run cartridge bearings into the ground and you won't damage anything else. It's just about riding pleasure and efficiency.

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1  
Your distances seem a bit low. 3,000 miles would be incredibly short life for a bottom bracket cartridge. 100,000 would be normal. Cup and Cone axles do wear quicker but that's more due to water ingress causing damage rather than wear from straight usage. – Criggie Apr 20 at 12:47

If your crank is wobbling or there's a noise in your bottom bracket when you're pedalling, maybe it's time for you to replace your bottom bracket.

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"noise from bottom bracket" can also mean loose chainring bolts or a broken frame, and is most often the former. – David LeBauer Mar 19 '12 at 3:18

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